Please help me understand MPI with Lexiscan.

Re MPI with Lexiscan injection, how is dosage controlled to avoid administering too much? What determines upper limit of stress induced? How long is heart stress elevated? How long is actual scan time? Am uncomfortable with an upcoming test — obviously. Thank you for any information & help.

Submitted by Regina from Long Beach, California

by Warren H. Moore, MD

Answering this question is a bit difficult because there are a number of different ways to perform this test depending on the patient’s clinical situation, the equipment that the facility uses, and the particular procedure chosen by the facility. The exact answer, therefore, would depend on you and the facility, but I can give a general answer that will cover most situations.

There are two medications given for a Lexiscan MPI study. One is Lexiscan (the brand name for regadenoson). This drug is given to simulate or augment the effects of stress by dilating blood vessels in the heart and allowing changes in blood flow to the heart to be assessed by pictures taken using the radiopharmaceutical. Lexiscan is given through an intravenous injection over approximately 10 seconds. Its effects on the heart occur quickly and last for about 10 minutes. During or shortly after this period, you may experience a feeling of shortness of breath, flushing, headache, or nausea. The severity of these symptoms varies between patients, but usually, no treatment is necessary and the side effects go away after a few minutes. Medication to reverse the effects is available, but is rarely needed. The dose of Lexiscan used is the same for all patients, based on research that was done years ago before the drug was approved by the FDA. There is no concern about an “overdose.” The amount of “stress” produced by the drug depends on exactly how your body responds to the drug and can’t really be predicted. In general, however, the effect lasts for 5-10 minutes and is quite tolerable for patients. Of course, as with all cardiac stress tests, there is a risk of severe reaction such as heart rhythm problems , chest pain, and even heart attack, but this risk is essentially the same whether you have a Lexiscan test or a treadmill test.

About 20-30 seconds after the Lexiscan is given, the other drug, a “radiopharmaceutical” (such as Cardiolite (sestamibi) or Myoview (tetrofosmin) is injected through the same IV line. This material allows images of the heart to be obtained, but has no other significant effect on the heart. This drug has its own side effects, but they are rare and except for a funny taste in the mouth for a few seconds, most patients never know they have had this injection. After this injection, there is a waiting period of 15-60 minutes before images are obtained. Obtaining the images takes 5-25 minutes depending on the exact equipment and protocol being used. Your local facility can give you more specifics about this for your test.

Some patients have only the “stress” test and imaging described above, but others require a second imaging procedure done without “stress.” This involves the injection of a separate dose of the radiopharmaceutical only and may be done before or after the “stress” test, but usually on the same day. Again, your local facility can best describe exactly what procedure they will use for you.